Our curriculum begins with a DNA extraction lab. This introductory lab lets your students examine and scientifically observe strands of DNA extracted from an organism, taking some of the mystery out of an abstract and difficult concept. Considering consistently good results and ease of preparation, we recommend the Carolina™ Plant Biotechnology: DNA Extraction lab. After performing the lab, students should make the following scientific observations:

DNA is linear.

DNA has a creamy white color.

DNA is soluble in water and insoluble in alcohol.

DNA is acidic.

Allow at least three 50-minute class periods for this lab.

Use the first class period for a prelab review of the structure and function of DNA.

Use the second class period for doing the lab.

Use the third class period to analyze and discuss the results.

The best learning about the structure and function of DNA often occurs when students work with DNA models. Students can create these models out of paper, marshmallows, gumdrops, pipe cleaners, Popsicle sticks, or plastic models. Now, however, there is a series of DNA model kits that are superb for building and manipulating DNA models. All your students, not just the kinesthetic learners, can benefit from these kits. You'll hear comments like, "Hey, I finally get it!"

This series of models, especially the first 3 (DNA Structure and Function, Transcription, and Translation) are designed to work together and build on each other. The fourth kit, Plasmid Biotechnology, can stand alone, but you'll enjoy having pieces from the other kits available to expand on the instructions. To give you a better idea of what these models can do in your classroom, let's take a close look at the first one in the series.

Using the DNA Structure and Function Molecular Model Kit, students, working individually or in cooperative learning groups, begin by identifying the individual pieces of a nucleotide and then assemble one model nucleotide using pieces from the kit. The kit contains enough pieces to build at least 30 model nucleotides. Students then matchup with a classmate that has the correct complementary model nucleotide to create one model base pair (bp).

Students learn that adenine (A) and thymine (T) form 2 hydrogen bonds while guanine (G) and cytosine (C) form 3 hydrogen bonds (A-T: 2 and G-C: 3). Using the sequence given in the instructions, students then assemble a model 15-bp DNA molecule by attaching the 5' end of one base pair to the 3' end of the adjacent base pair. They learn that a DNA molecule grows in a 5' to 3' direction. Finally, students hold the DNA model up and twist it to form the famous double helix.
Having made a model DNA molecule, students experience how DNA replicates and forms exact copies of itself for cell division (mitosis). There are extra model nucleotides already available that some students made which did not fit into the sequence called for in the instructions. Additional nucleotides are removed from the model DNA molecule to have enough for demonstrating DNA replication.

Students unwind the double helix model and then "unzip" it by breaking apart the hydrogen bonds at one end to form a replication fork. The remaining hydrogen bonds are broken until there are 2 separate strands of model DNA. Next, students attach succeeding complementary bonds to the lower strand of the replication fork. Discuss Okazaki fragments as students replicate the upper strand of the molecule.

Eventually, students wind up with 2 model DNA molecules that are exact copies of each other and are both exactly like the parent. This is a good opportunity to introduce and discuss the semiconservative theory of DNA replication. As your students work with the models, emphasize the roles they play as they act as enzymes and perform the various actions necessary for DNA replication to occur.

This model-based, learn-by-doing method is what really reinforces these abstract, difficult concepts. You can disassemble and reassemble the kit over and over within one class or share it among several biology teachers. These kits are a tremendous pre and post activity for teaching DNA structure and function.

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